The invention relates to a method and apparatus for open-end friction spinning with two friction rollers, driven in the same rotational direction and adjacently arranged to form a yarn forming wedge-shaped gap therebetween with a suction device effective in the area of the wedge-shaped gap. A fiber feed channel leads from an opening and feeding device to the wedge-shaped gap, which channel extends at a sharp angle to the gap. A yarn withdrawal device is provided for drawing off the produced yarn in the direction of the extension of the wedge slot.
An important problem with open-end friction spinning machines of the above-mentioned kind is that the fibers should be deposited within the wedge-shaped gap in a straight and parallel manner because the quality of yarn produced is highly dependent on such deposition of the fibers.
A known device of the above-mentioned type disclosed in German Published Unexamined Application (DE-OS) No. 28 10 184 has a fiber feed channel which is steadily widened up to the feeding mouth or opening opposite the wedge-shaped gap. It is thereby attained that the fibers leaving the opening roller in an extended or straightened manner make a pivotal motion and arrange themselves parallel to the wedge shaped gap. However, this method does not consider that along with the steadily widening of the fiber feed channel, also the speed of airstream necessary for transportation of the fibers decreases so that the trailing ends of the fibers accelerate faster than the leading ends. This leads directly after a very short transportation distance to a tangled position of the fibers within the fiber feed channel making it impossible to have a controlled and orderly fiber deposition in the yarn forming gap.
A principal problem involved in a straightened and orderly deposition of fibers within the wedge-shaped gap results from the fact that under normal conditions the transportation speed with which the fibers are fed in is substantially faster than the drawings off or withdrawal speed of the produced yarn. Under these conditions, the incoming fibers reaching the yarn forming gap are slowed down so that they are shoved or buckled resulting in a hairpin-like distortion of the fibers.
It is an object of this invention to provide a device of the above-mentioned type with optimum straightened parallel fiber deposition within the yarn forming gap.
This object is achieved by the invention providing that the mouth of the fiber feed channel is widened in the area of the yarn forming gap and providing that the fiber feed channel wall facing away from the yarn forming gap is configured with a convex curve shape.
Through this one-sided widening of the fiber feed channel in the area of the feeding mouth by means of slightly sloped curve, the air stream necessary for fiber transportation is changed whereby the fibers somewhat follow the change in slope directed over and above from the yarn forming gap so that the same reach this gap subsequently with both of their ends almost at the same time. A shoving/buckling of the fibers is thereby no longer to be expected despite the lower draw off speed of the yarn to be produced.
In advantageous preferred embodiments of the invention, the channel wall opposite the wedge-shaped yarn forming gap forms a convex curvature towards this gap with a constant turning radius. It is thereby advantageous if the end of the channel wall facing the gap is formed parallel to the longitudinal direction of the gap. Thereby, the entire length of the mouth area is utilized for straightening out of the fibers.
In an advantageous arrangement of the invention it is provided that the fiber feed channel is arranged essentially to extend in the withdrawal direction of the yarn to be produced. Thereby, the fibers are withdrawn in the same direction as they are fed in so that fiber buckling due to a turn around of the fibers is avoided. Due to the curved channel wall and the turning of the fibers due to the turning of the airstream, buckling of the fibers is avoided in spite of the slowdown of the incoming ends of the fibers.
The fiber channel up to the area of the feeding mouth preferably consists of an almost constant, advantageously groove-like cross section. It is thereby assured that the fibers that leave the feeding and opening device in a straightened position will also remain in said position up to the area of the mouth and then first obtain the desired curvature or bending. It is advantageous according to especially preferred embodiments to configure the length of the fiber feed channel to be larger than the average fiber length of the staple fiber material that is being processed and preferably is about twice the length of the average staple length. The fiber feed channel thereby performs an additional straightening effect.
It is also advantageous according to a further development of preferred embodiments of the invention to configure the total length of the mouth of the fiber feed channel in the direction to the gap corresponds to at least the average length of the staple of the fiber material to be processed. It is thereby attained that almost all fibers are turned within the area of the mouth corresponding to the widening of the channel and are evenly deposited in the yarn forming gap.
In yet a further development of the invention, it is provided that the suction device is adaptable to different suction effects at various locations in longitudinal direction of the yarn forming gap, whereby a higher suction effect is obtained in the area of the rounded channel wall. It is thereby further possible to support the turning of the airstream along the curved channel wall and as a result the turning of the fibers. In a further development of the invention it is provided that the area of the mouth of the fiber feed channel includes a device for producing an additional air stream which is essentially directed in the longitudinal direction of the yarn forming gap toward the rounded or curved channel wall. This additional air stream strengthens the turning of the transportion air stream and thereby the adjustment of the fibers to be fed along the wedge gap and the curved channel wall so that the straightened deposit of fibers is further improved.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purposes of illustration only, embodiments in accordance with the present invention.